Look at the attached diagram of a simple telegraph system (see attachment). The battery supplies 48 volts and the receiver coil has a resistance of 600 ohms. A current of 20 mA must flow in the receiver coil to achieve reliable operation. 26 gauge wire with a loop resistance (the resistance of both conductors added together) of 268 ohms / km is used to connect the sending station to the receiving station.
A. What is the maximum length of the link, in km, that guarantees reliable operation?
B. How much power is dissipated in the receiving station coil when the key at the sending station is closed?
C. How much power is dissipated in the 26 gauge wire when the key at the sending station is closed?
This posting contains the solution to the given simple telegraph system problem.